1. Field of the Invention
The present invention relates to a substrate coated with a non-stick coating.
2. Prior Art
Non-stick coatings are well known in the art. In these coatings normally fluorocarbon resins are used, since these resins have a low surface energy as well as thermal and chemical resistance. However, non-stick coatings solely based upon fluorocarbon resins suffer from poor adhesion to the substrate and poor scratch and abrasion resistance. Such coatings are easily damaged when cut with a knife or another metal tool. Rubbing or sanding also easily wears these coatings away.
It is known in the art that the adhesion can be improved by roughening of the (metal) substrate, e.g. by grinding, sand blasting, acid etching, brushing or baking a rough layer of glass, ceramic or enamel frit onto the substrate. This is disadvantageous since it is an additional step in the manufacturing process, which can be time consuming and/or requires the heating of the substrate.
To improve the adhesion to substrates and the mechanical properties (in particular, scratch resistance and abrasion resistance) of these coatings, the fluorocarbon resin is mixed with one or more heat resistant binder resins for better adhesion and one or more pigments and/or fillers for coloring and improvement of the mechanical properties.
Non-stick coatings may be applied in a single layer or as a multilayer coating.
U.S. Pat. No. 6,291,054 describes a multilayer non-stick coating wherein the undercoat (primer) comprises a mixture of a fluorocarbon polymer, a heat resistant binder, and large hard ceramic particles. The topcoat comprises a fluorocarbon resin. In the undercoat the heat resistant binder should improve the adhesion to the substrate, the fluorocarbon resin should improve the adhesion between the primer and the topcoat, and the large hard ceramic particles should improve the mechanical properties. However, the presence of the fluorocarbon resin (which has non-stick properties) lowers the adhesion of the primer to the substrate and the adhesion of the ceramic particles within the primer layer.
In WO 02/14066 a single layer non-stick coating is disclosed. This single layer comprises a binder resin, a fluorocarbon resin and filler material. However, this single layer non-stick coating has the same disadvantages as the three-component primer layer described above.
Surprisingly it was found that in a multilayer non-stick coating good adhesion between the primer layer and a next coating layer that is applied on top of the primer layer comprising a fluorocarbon resin can be obtained if the primer layer comprises a heat resistant binder and is substantially free of fluorocarbon resin. Therefore, the primer layer shows optimum adhesion to the substrate and to optionally present particles to improve the abrasion resistance of the coating, whereby the adhesion to the next coating layer is not compromised.